1. Field of the Invention
The present invention relates to a method of connecting a semiconductor chip such as IC or LSI to a wiring tape or so-called TAB (Tape Automated Bonding) tape used for connection of the semiconductor chip to a substrate or a lead frame and also relates to a bump sheet and a bumped tape which are used in such a connection method.
2. Description of the Related Art
Conventionally, as a common practice, a semiconductor chip such as IC or LSI is supported by a lead frame and a chip circuit is connected to the lead frame by means of Au bonding wires or the like.
In recent years, however, as semiconductors implement their high performance, a demand for remarkably high density in assemblying has been increased. Namely, as a result of higher density in integration of elements in an integrated circuit and a greater demand for highly developed assembly technique associated therewith, it has followed that the conventional wire bonding technique in wiring of a chip circuit cannot cope with such a demand in many cases.
A TAB system is a bonding method which copes with the above-mentioned recent demand and hence has widely been put to practical use as a method of bonding the electrodes of a semiconductor chip. In a bonding method based on the TAB system, a TAB tape having lead patterns formed in series thereon is used instead of the lead frames used in the wire bonding method and bumps preliminarily formed in either lead portions on the TAB tape or bonding portions on the side of the chip are substituted for the bonding wires. The actual bonding is generally carried out by means of a thermocompression bonding method or the like with the chip and the TAB tape being superposed on each other.
FIG. 12 is a schematic view showing one example of the TAB type of bonding. In the figure, reference numeral 1 designates a semiconductor chip on which a plurality of bumps 6 are preliminarily formed. Numeral 2 designates metallic leads which form a TAB tape 12 together with a tape-like resin film 3. The chip 1 is placed on a bonding stage 4 of a TAB bonder with the bumps 6 upside and the TAB tape is placed above the chip 1. In this state, the bonding is carried out in such a manner that a bonding tool 5 having a proper heat is pressed down from the upside in a direction indicated by arrow.
Usually, the TAB tape used in the above method, is fabricated by providing sproket holes and a device hole in a film made of a synthetic resin such as polyimide or polyester, laminating a metal foil on the film and thereafter forming a lead pattern by means of a photoresist method.
On the other hand, the bumps for connection of the TAB tape and electrodes of the semiconductor chip such as IC or LSI are formed in many cases by applying a plating on Al electrodes of the semiconductor chip, as disclosed by Electronic Parts and Materials, Jul. 1989, p. 71. However, the formation of bumps on the Al electrodes of IC or LSI through the plating method is high in cost and involves a damage of the semiconductor chip circuit during the bump forming work and hence is not necessarily recommended.
Also, as a method of forming bumps on leads on the side of a TAB tape, there is a method disclosed in JP-A-62-28623 or a "transferred bump TAB method" disclosed in National Technical Report, Vol. 31, No. 3, Jun., 1985, pp. 116-124. In the transferred bump TAB method, bumps are preliminarily placed with a predetermined pattern on a glass substrate and are transferred to leads of a TAB tape in which a lead pattern is formed. But, this method, too, involves a complicated work and a problem in cost.